1. The Field of the Invention
The present invention relates generally to composite tubes, and more particularly, but not exclusively, to filament-wound, composite tubes having structural properties that satisfy certain standards of strength and durability for use as a street light pole.
2. Description of Related Art
Structural columns for supporting street lights, referred to herein as “light poles,” must satisfy the standards put forth by the American National Standards Institute (“ANSI”) in certain applications. One of these standards mandates that material used in the construction of light poles must pass the following test: a section of the pole material is cut to be twenty feet in length, is then cantilevered at one to extend outwardly in a horizontal direction as shown in FIGS. 1-2. A 300-pound load is then applied downwardly at the free end. The lateral (vertical) deflection at the free end responsive to the 300-pound load must not exceed 19.938 inches under current standards. These and other rigorous ANSI standards have heretofore necessitated that light poles often be made from structural steel.
Composite material is lighter and less expensive than structural steel, and attempts have been made to construct utility poles and light poles from composites. Unfortunately, such attempts have not been found to meet the ANSI standards. For example, U.S. Pat. No. 2,870,793 (granted Jan. 27, 1959 to Bailey), which discloses a composite utility line support member, admits to a breaking load of only 62 pounds (see col. 8, lines 72-74). U.S. Pat. No. 3,429,758 (granted Feb. 25, 1969 to Young) teaches a composite light pole utilizing a core material of rigid foam for providing structural reinforcement to the pole (see col. 2, lines 59-62, and FIG. 2a). U.S. Pat. No. 4,436,781 (granted Mar. 13, 1984 to Rother et al.) is directed to a simple street lamp having a support pole made of composite material and focuses on a better way to connect the lamp to the pole. None of these prior art patents, nor any other prior art information known to applicant, teaches or suggests a filament-wound pole capable of satisfying high-strength standards with structural aids or reinforcements.